1. The Future of Dark-Matter Axion Searches
Darin Kinion
(LLNL/UC Berkeley)
December 9, 2004

2. Axions and the Strong-CP Problem

3. Axion properties

4. The “axion window”
The parameter space is bounded both in mass and coupling constant.

5. How to detect dark-matter axions (Sikivie, 1983)

6. Axion Dark-Matter Experiment (ADMX)
Located at LLNL (Livermore, CA)
ADMX Collaboration – LLNL, UF, UCB and NRAO
Started data taking in February 1996.

7. ADMX receiver and data
candidates
world’s quietest radio receiver
Data from 725 – 800 MHz
To date, all candidates have either disappeared upon re-scanning or have been linked to external interference

8. Current ADMX limits Particle Physics Astrophysics
ra » rhalo ¼ 0.45 GeV/cm3
Definitive experiment requires relaxing the constraint on the axion halo density as well as achieving sensitivity to DFSZ model axions.

9. The ADMX upgrade plan
Goal : Increase the sensitivity (scan rate) by lowering the system noise temperature
1.5 K pumped LHe
2.0 K GaAs HFET amp
Phase I – Improve TN with lower noise microwave amplifiers
Phase II – Improve Ts with a dilution refrigerator

10. Phase I Upgrade – SQUID Amplifiers

11. Microstrip amplifiers

12. ADMX hardware design for Phase I
1K Pot
Cavity
Main Magnet
50 cm
Field-free region
Field cancellation coil
Force compensation coil
Longitudinal field on axis

13. Summary of ADMX
Current experiment is sensitive to KSVZ axions if they dominate the local galactic halo density
Phase I upgrade is underway to improve sensitivity by replacing GaAs HFET amps with SQUIDs.
Phase II upgrade would provide an order-of-magnitude improvement in sensitivity by cooling the cavity and SQUID to < 100 mK.
Long-term development plan involves higher-frequency cavities and amplifiers.

14. Other axion searches The Kyoto Rydberg Atom detector
The CERN Axion Solar Telescope
Sun
CERN

15. Summary of axion exclusion regions
CAST (projected)
ADMX Upgrade

16. Summary
The Peccei-Quinn mechanism remains the most compelling solution to the Strong-CP problem in QCD
ADMX is currently exploring the lowest decade of the axion window at KSVZ sensitivity
The goal of the two-phase ADMX upgrade is to cover the lowest two decades of the axion window with sensitivity to DFSZ axions comprising a fraction of the galactic halo